1. Field of the Invention
This invention relates to trilithium phosphate isomerization catalysts and, more particularly, to a method of enhancing catalyst activity.
2. Background of the Prior Art
Trilithium phosphate (Li.sub.3 PO.sub.4) is useful as a catalyst in the isomerization of alkylene oxides to their corresponding alcohols, particularly propylene oxide to yield allyl alcohol: ##STR1##
Several side reactions normally compete with the desired isomerization reaction, leading to the formation of compounds like propionaldehyde (CH.sub.3 CH.sub.2 CHO), 1-propanol (CH.sub.3 CH.sub.2 CH.sub.2 OH), and acrolein (CH.sub.2 CHCHO). It is desirable, of course, that the trilithium phosphate isomerization catalyst minimize formation of these byproducts.
The activity or efficiency of trilithium phosphate catalysts used for such purposes is ordinarily evaluated by its ability to convert a maximum amount of propylene oxide and to produce a high yield of allyl alcohol product with minimal byproducts. Conversion, a measure of the percentage of propylene oxide feed isomerized by the catalyst, is calculated thus: ##EQU1##
Selectively, a measure of the purity of the allyl alcohol product that is expressed as a percentage, is calculated thus: ##EQU2##
The amount of 1-propanol byproduct formed along with allyl alcohol is desirably minimized in the product. This is because separation of 1-propanol (B.P. 97.2.degree. C.) from the allyl alcohol (B.P. 96.9.degree. C.) by distillation is not easily accomplished due to their similar boiling points. The 1-propanol byproduct is expressed as a weight percentage of the allyl alcohol in the product, being calculated thus: ##EQU3##
A satisfactory trilithium phosphate catalyst is generally one which has a conversion of at least 40%, a selectivity of at least 90% and which produces no more than than 1% 1-propanol.
Various techniques are described in the patent literature for regenerating or reactivating trilithium phosphate catalysts. Activation/regeneration procedures applicable to trilithium phosphate catalysts are taught in U.S. Pat. Nos. 3,090,816 and 3,092,668, which involve treatment of the catalyst with various organic solvents at elevated temperature. U.S. Pat. No. 3,090,815 teachs an analogous treatment with water, at temperatures of from 50.degree.-250.degree. C. but notes that electrolyte-free water (e.g., distilled or demineralized water) is desirably used to avoid catalyst deterioration from the ion species.
These catalyst regeneration/activation techniques, however, have not been shown to improve trilithium phosphate catalyst efficiency such that 1-propanol byproduct formation is maintained below satisfactory levels.